Research articles

Proteins from bone extracellular matrix are known to mediate the organization of apatite crystals in bone. Now, electron microscopy, X-ray scattering and nuclear magnetic resonance measurements of the structure and organization of apatite nanoparticles and intact bone samples show that water also plays a significant role in orienting the apatite crystals, and that such structuring is mediated by a disordered mineral layer that coats the crystalline core of bone apatite.

Size effects and geometry can significantly modify the properties of nanoparticles with direct impact on their biocompatibility and chemical reactivity. Using high-resolution electron microscopy it is now shown that strain gradients induced in the oxide shell of cuboid Fe nanoparticles can lead to oxide domain formation and shape evolution of the particles.

Compared with their rigid counterparts, thin-film solar cells grown on flexible substrates usually display lower power-conversion efficiencies. Now, the application of a post-deposition alkaline treatment that modifies the chemical composition of the surfaces of Cu(In,Ga)Se₂ thin films reduces optical losses in these flexible photovoltaic architectures. Furthermore, efficiencies comparable to solar cells based on polycrystalline silicon are achieved.

Metal fluorides/oxides are promising electrodes for lithium-ion batteries, but the mechanism by which they exhibit additional reversible capacity is still not well understood. By using high-resolution solid-state NMR techniques it is shown that extra capacity in this RuO₂ system is due to the generation of LiOH and its subsequent reversible reaction with Li to form Li₂O and LiH.

In organic semiconductors, disorder-induced traps can alter the mobility of the charges and introduce noise in transport measurements. It is now shown that simple drop-casting of perfluoropolyether on top of organic single-crystals is an effective strategy for healing charge traps. This method allows the intrinsic transport properties of these materials to be recovered as well as suppressing noise in Hall effect measurements.

Rare-earth hexagonal manganites are known for their multiferroic properties. Using parameters calculated from first principles, a theoretical description of the topological defects arising in these systems is now presented.

Somatic cells can be reprogrammed into induced pluripotent stem cells biochemically through the expression of a few transcription factors. It is now shown that aligned microgrooves or nanofibres on cell-adhesive substrates can promote the reprogramming of somatic cells more efficiently through epigenetic regulation of genes related to pluripotency and the mesenchymal-to-epithelial transition. The findings suggest that the epigenetic state can be regulated by variations in cell morphology.

Cells can sense and respond to their environment through mechanical forces. However, how the cell’s cytoskeleton transmits forces and how cytoskeletal proteins respond to forces is largely unknown. Now, a combination of mechanical perturbations and multiscale modelling offers insights into the molecular mechanisms behind the observed variations in the accumulation kinetics of the involved proteins in response to different types of deformation.

Spin-torque diodes enable the detection and rectification of radiofrequencies by means of spin-torque-induced ferromagnetic resonance between nanomagnets. Now, by using magnetic tunnel junctions with a MgO barrier and a FeB free-layer detection sensitivities in excess of those of semiconductor devices are demonstrated.

Patterning physiologically relevant proteins in three-dimensional hydrogels without affecting the activity and stability of the proteins has been difficult. Now, by using enzymatic crosslinking reactions, in situ control over the phototriggered immobilization of virtually any desired protein in a synthetic hydrogel is demonstrated. The approach can be used to manipulate cells, as demonstrated by the three-dimensional control of the invasion of mesenchymal stem cells within poly(ethylene glycol) hydrogels.

Previous studies have suggested that even in the absence of a graphene bandgap, a relaxation bottleneck at the Dirac point may allow for population inversion and lasing. Now, using time- and angle-resolved photoemission spectroscopy with femtosecond extreme-ultraviolet pulses, it is shown that interband excitations give rise to population inversion, suggesting that terahertz lasing may be possible.

Although metals cannot be ferroelectric in the strict sense of the term, it has long been predicted that they can undergo structural transitions that share similarities with ferroelectricity. LiOsO₃ is now shown to be an experimental realization of such a ferroelectric-like metal.

Clathrate materials have been the subject of intense investigation because of their beneficial properties, in particular their low thermal conductivities. Now, improved thermopower at high temperatures arising from strong electron correlation effects has been achieved in a type-I clathrate containing cerium guest atoms.

A strategy for assessing blood microcirculation and tissue hydration relies on monitoring the temperature and thermal conductivity of skin, respectively. It is now shown that arrays of micrometre-sized sensors and heaters can be integrated on stretchable substrates that conformably adhere to the skin; these devices allow spatially resolved heating and real-time temperature mapping in patients without limiting their motion.

The emergence of conductivity at the {001} interface of LaAlO₃ and SrTiO₃ is one of the more celebrated examples of interface engineering. Using a microscopy approach based on a sensitive magnetometry probe, it is now shown that narrow paths of enhanced conductivity occur along the crystallographic axes of the oxide structures.

Hard biological materials such as diatoms and sea sponges can inspire the design of structural materials that are mechanically robust yet lightweight. Hollow titanium nitride lattices have now been fabricated that mimic the length scales (from 10 nm to 100 μm) and hierarchy of biological materials. These lattices attain tensile strengths of 1.75 GPa without failing (even after multiple deformation cycles) because of the low probability of pre-existing flaws.

Although rechargeable lithium–air batteries are receiving significant attention because of their high theoretical specific energy, carbon cathodes that are currently used decompose during oxidation and promote electrolyte decomposition on cycling. A titanium carbide-based cathode is now shown to reduce side-reactions, and exhibits enhanced reversible formation and decomposition of Li₂O₂.

For alloys displaying diffusive transport behaviour, understanding the electrochemical factors that control dealloying-induced morphologies could prove important for battery development. Composition, particle size and dealloying rate are now shown to affect morphology evolution in the Li–Sn system, and dealloying is found to be governed by both percolation-dissolution and solid-state-diffusion mechanisms.

Sodium cobaltate has latterly received attention due to its appealing thermoelectric properties. By combining inelastic X-ray and neutron scattering results with detailed first-principles calculations, it is now shown that low-energy rattling modes of sodium ions within multi-vacancy clusters play a central role in determining the low thermal conductivity of this material.

Low-temperature redox reactions in solids resulting in no thermomechanical degradation can be used to enhance the performance and lifetime of energy devices. Rapid and reversible redox activity has now been demonstrated at temperatures as low as 200 °C in both epitaxially stabilized oxygen-vacancy-ordered SrCoO_2.5 and thermodynamically unfavourable perovskite SrCoO_3−δ single-crystalline thin films.